1. Field of the Invention
The present invention is directed to a method and apparatus for producing a continuous extrusion molding product with a varying profile. More particularly, the present invention is directed to a molding machine having shaping knives rotatable around axes substantially non-parallel to the flow direction of the extruded material.
2. Description of the Related Art
Molding products are useful for sealing spaces between, for example, the edge of a windshield and the body panel of a vehicle. In the case of automobile windshield molding, it is well known in the art that varying the profile of a molding strip along its length can obtain various advantages, for example the formation of water-draining channels for receiving water flowing on the surface of the windshield. Numerous designs for automobile windshield molding strips with a varying profile have been proposed.
FIGS. 1 and 2 illustrate one example of a molding strip with a varying profile for sealing the space between a windshield and an opening in the frame of a vehicle body. Molding strip 2 is a continuous plastic strip comprising three sections: an upper section 2A mounted between the upper edge of the windshield 11 and the roof panel 12, a side section 2C mounted between the side edges of windshield 11 and the pillar panels 13, and corner sections 2B joining the upper section 2A with side sections 2C at the corners of windshield 11. Molding strip 2 comprises exterior wing 21 including an inward wing portion 21a and an outward wing portion 21b, connecting portion 22, and foot 24.
Outward wing portion 21b is for covering the periphery of the vehicle body panels 12, 13 and is of uniform thickness along its length. As illustrated in FIG. 2, the profile of molding strip 2 varies along the length of side section 2C such that inward wing portion 21a gradually thickens from corner section 2B to the central portion of side section 2C. As inward wing 21a thickens, connecting portion 22 lengthens and sub-inward wing 21c diverges from inward wing 21a to form water drain channel 28. Water drain channel 28 gradually widens and deepens towards the center of side section 2C and then gradually becomes thinner and shallower towards the lower extreme of side section 2C. The profile of corner section 2B is the same as that of upper molding 2A; the flexible quality of molding 2 allows it to be deformed and fitted around the corner of windshield 11. Metal wire 23 is embedded in molding strip 2 to reinforce the strip.
FIG. 3A shows a cross-sectional view of molding strip 2 installed between windshield 11 and roof panel 12. FIG. 3B shows a cross-sectional view of molding strip 2 installed between windshield 11 and a central portion of pillar panel 13. In FIG. 3A, the windshield 11 is received between foot 24 and inward wing 21a. In FIG. 3B, connecting portion 22 is lengthened and windshield 11 is received between sub-inward wing 21c and foot 24. A water drain channel 28 is formed between inward wing 21a and sub-inward wing 21c. 
FIGS. 4 and 5 illustrate a prior art molding machine 3 for producing the molding strip 2. Molding machine 3 comprises die 31 and shaping knives 32 and 33. In FIGS. 4 and 5, plastic material to be extruded flows in a direction perpendicular to the plane of the illustrations. Die 31 is stationary and has an opening 34 in the shape of a vertically long rectangle, where the upper portion of the rectangle corresponds to the cross-sectional profile of exterior wing 21. Specifically, the contour of portion 341 corresponds to the cross-sectional profile of outward wing 21b, the contour of portion 343 corresponds to the cross-sectional profile of inward wing 21a, and the contour of portion 345 corresponds to the cross-sectional shape of sub-inward wing 21c. 
Shaping knives 32, 33 are rectangular plates supported by guides 32a and 32b, respectively, and are movable in the plane of the illustration, e.g., movable in a plane perpendicular to the flow direction of the plastic material to be extruded. Shaping knife 32 has an opening 35 with a contour corresponding to the cross-sectional profile of foot 24. When in a first operational position illustrated in FIG. 4, shaping knife 32 is positioned on die 31 such that the openings 34, 35 are in the cross-sectional shape of molding strip 2 before inward wing 21a is thickened. As the plastic material is extruded, shaft 32d connected to a converter 32b and motor 32c gradually moves shaping knife 32 to a second operational position illustrated in FIG. 5 such that inward wing 21a is thickened. A reciprocal motion is performed to cause inward wing 21a to become gradually thinner.
Shaping knife 33 has a slanted edge 331 with a contour corresponding to the cross-sectional profile of water drain channel 28. When in a first operational position illustrated in FIG. 4, shaping knife 33 is positioned outside of the flow of the plastic material. As the plastic material is extruded, shaft 33d connected to a converter 33b and motor 33c gradually moves shaping knife 32 to a second operational position illustrated in FIG. 5 such that water drain channel 28 is formed. A reciprocal motion is performed to cause water drain channel 28 to become gradually less deep and thinner.
FIG. 6 illustrates another molding machine 100 of the prior art in which die 104 rotates about pin 103 in a plane perpendicular to the flow of the plastic material to be extruded such that the cross-sectional shape of opening 104a is changed during extrusion of the plastic material.
The molding machines of the prior art are able to produce molding products with varying profiles. However, because the movement of the dies is in a plane perpendicular to the flow of the plastic material, the streamlines of the flow of the plastic material around the edges of the dies are significantly disrupted, thereby causing wrinkles on the final product. Furthermore, sudden pressure changes in the portions of the flow may result in stagnation points where plastic material is trapped and hardened. This also results in wrinkles and even burrs on the final product. Finally, the movement of the dies between operational positions in the molding machines of the prior art causes a sudden increase in flow pressure against the dies. As a result, the parts of the molding machine suffer fatigue and wear-and-tear.
It is therefore an object of this invention to provide a method and apparatus for producing a continuous extrusion molding product with a varying profile, in which the molding machine has shaping knives rotatable around axes substantially non-parallel to the flow direction of the molten material to be extruded.
It is another object of this invention to provide a method and apparatus for producing a continuous extrusion molding product with a varying profile, in which the rotation of shaping knives around axes perpendicular or oblique to the flow direction of the molten material to be extruded allows the contour of the opening between the dies to be manipulated across a gradient of shapes and sizes to produce a smooth change in profile of the molded product.
It is yet another object of the invention to provide a method and apparatus for producing a continuous extrusion molding product with a varying profile, in which disruption of the flow and sudden pressure changes in portions thereof caused by the movement of shaping knives is significantly reduced, thereby reducing wrinkles and burrs on the final product.
According to a first aspect of the present invention, there is provided a molding machine for producing a molding product with varying profile comprising: a die with an inlet for receiving molten material, a channel, and an outlet, the channel directing the molten material from the inlet to the outlet along a first axis; a first shaping knife, rotatable around a second axis non-parallel to the first axis between a first operational position and a second operational position, the shaping knife having a first molding surface; and a second shaping knife, rotatable around a third axis non-parallel to the first axis between a first operational position and a second operational position, the shaping knife having a second molding surface; whereby the first and second molding surfaces together define a first contour in the outlet when the first and second shaping knives are in their first operational positions, and define a second contour in the outlet when the first and second shaping knives are in their second operational positions. In a preferred embodiment, the shaping knife is rotatable around an axis perpendicular to the first axis while the shaping knife is rotatable around an axis oblique to the first axis. Both shaping knives have leading edges which are wedge shaped to more easily cut into the flow of molten material. Molding surfaces may also be provided in the outlet.
In the preferred embodiment, the molding product is automobile windshield molding have an outer wing portion, an inner wing portion, a connecting portion and a foot. the profile of the inner wing portion varies between a first profile in which in the inner wing portion has a first thickness and a second profile in which the inner wing portion has a second thickness thicker than the first thickness. A water channel is formed in the inner wing portion of the second profile. Generally, the contour of the first molding surface corresponds to the profile of the foot, the contour of the second molding surface corresponds to the profile of the water drain channel, and the contour of the molding surface on the outlet corresponds to the outer wing. When the first and second shaping knives are in their first operational positions, the contour of the outlet corresponds to the first profile, and when the first and second shaping knives are in their second operational positions, the contour of the of the outlet corresponds to the second profile.
According to a second aspect of the present invention, there is provided a method of producing a continuous extrusion molding product including the steps of: extruding molten material though an opening in a die when first and second shaping knives are in a first operational position together defining a first contour in the opening to form a molding product with a first profile; and gradually rotating the first shaping knife about a first axis perpendicular to the flow direction of the molten material to a second operational position and gradually rotating the second shaping knife about an axis oblique to the flow direction of the molten material to a second operational position, the second operational positions of the first and second shaping knives defining a second contour in the opening, to alter the profile of the molding product across a gradient range of intermediate profiles to a second profile. The molten material is thermoplastic resin, elastomer, or foam resin. An additional step of rotating the first and second shaping knives from their second operational positions to the first operational positions may also be performed.
The method and apparatus of the present invention is suitable for molding any molding product with a profile that varies along its length. Examples of molding products for which the method and apparatus of the present invention is suitable are automobile windshield molding, plastic rope and mats, and architectural frame molding.
In the molding machine of the present invention, the shaping knives are rotated about axes perpendicular or oblique flow to the flow direction of the molten material to be extruded; thus, the intrusion of the shaping knives into the flow of molten material is smoother than that of the dies of the prior art. As a result, the disruption of the streamlines of the flow of the molten material around the edges of the dies is significantly reduced, thereby reducing or even eliminating wrinkles on the final product. This effect can be enhanced by using shaping knives with leading edges having a wedged profile.
In addition, sudden pressure changes in the portions of the flow resulting in stagnation points in the flow are avoided, thereby eliminating the problem of molten material being trapped and hardened in the molding machine of the present invention.
Finally, because the movement of the shaping knives between operational positions cuts into the flow of molten material in a smooth fashion, there is no sudden increase in flow pressure against the shaping knives. As a result, the parts of the molding machine suffer less fatigue and wear-and-tear than those in the prior art.